Advanced, high-performance engines will require improved performance main shaft bearing compartment seals while also being required to meet more aggressive cost, weight, size, and reliability metrics. Improved capability main shaft bearing compartment carbon seals are needed to meet the increased demands of next generation high-performance engines. Carbon seals enable an engine and bearing compartment to function with minimal impact on Thrust Specific Fuel Consumption (TSFC), a thermal management system (TMS), and a lubrication system. Current and future engines require seals capable of providing wear resistance, improved performance and improved reliability.
Referring to FIG. 1A, an environment is depicted of a system that may be applied in connection with a bearing compartment 101 of an engine. In FIG. 1A there are six ring seal stages, denoted as stages 1 through 6, arranged about an engine centerline 102. A pair of adjacent ring seal stages (e.g., stages 1 and 2) are bounded on either side by a pair of plates (e.g., plates 104 and 106) and a liner 108 located radially outward from the engine centerline 102. Also associated with the environment of FIG. 1A are two rotors; a so-called high rotor 110 and a low rotor 112. The two rotors 110 and 112 may rotate in the same direction or in opposite directions, with the same speed or with different speeds. Aspects of this disclosure are not limited to a co-rotating environment; for example, aspects of the disclosure may be applied in connection with a rotating structure arranged about a fixed/stationary structure.
FIG. 1B illustrates a pairing of any two adjacent stages (e.g., stages 1 and 2, or stages 3 and 4, or stages 5 and 6) of FIG. 1A. Between the two stages shown in FIG. 1B exists a cavity 152 for accommodating a retaining spring which loads these stages against the aforementioned plates (e.g., plates 104 and 106), causing contact pressure against them. Stages 1, 3 and 5 may contain higher levels of axial force, contact pressure and PV (contact pressure (P) multiplied by rubbing velocity (V)) levels compared to stages 2, 4 and 6. This is due to the additional air pressure loading imparted onto stages 1, 3 and 5. Stages 2, 4 and 6 also contain air pressure loading, however this pressure acts in the opposite direction so as to reduce the overall axial force, contact pressure and PV.
The existing design of the six carbon ring elements contains a relief cut notch (e.g., notches 155 and 156—see FIG. 1B) on the inner diameter (ID) sealing face, which was set to avoid the adjacent seal plate radius edge (e.g., edge 132 of FIG. 1A) with radial eccentric overhang and a potential to cause a wear step in the carbon element. The need to avoid the seal plate radius edge only applies to stages 2, 4 and 6; however, the carbon element relief cut notch (e.g., notch 155 or notch 156) is provided on all 6 carbon ring stages 1-6 to maintain proper “fool-proofing” (e.g., to avoid improper assembly/installation). It may be possible to remove this relief cut notch (e.g., 155) on stages 1, 3 and 5 since these particular stages do not require it, as the adjacent seal plate geometry does not contain a radius edge. However, such an approach makes the two stages in each pair different from each other, raising concerns for fool-proofing and the possibility that the incorrect ring would be placed in the incorrect location, potentially causing premature carbon ring wear and failure.